Homework Help:
Help absolute value proof?

3. The attempt at a solution
all i've gotten to so far is this : la+bl < 2c
lal + lbl < 2c
we have : la+bl < lal+lbl
then la+bl < 2c
i need to prove that la-bl < 0.?
also by squaring all i gotten so far is (la+bl + la-bl)/2 < 2c...